Holloway,
First thing, learning to fly is one of the most expensive bits, as a rule of thumb to get your basic license you'll need about £2000 for a microlight PPL, £4000 for a light aircraft PPL, and about £7,000 for a helicopter PPL.
After that, maintaining minimum legal currency, and being safe, are two totally different things. I'm sure most people will agree here that 2-3 hours per month is a sensible minimum to be a safe pilot.
Assuming that you can afford the initial PPL course, you've got various options:-
Hiring, expect about £50/hr for a microlight (not currently possible, but should be before too long I'm told), about £90/hr for a straightforward light aircraft, about £160/hr for a straightforward light helicopter. There's no effective upper limit.
If you can afford to buy (and you can get basic microlights or small shares in light aircraft for anything upwards of £2k) the running costs get better. Running costs will start at around £25/hr for a microlight, £40/hr for a syndicated light aircraft, £120/hr for a syndicated light helicopter (these are fairly rare mind you). Again there's no real upper limit, it just depends what you're flying, and on an element of luck.
Personally, I run a 2-seat microlight which at about 40hrs/yr works out at about £25/hr, and a share in a 4-seat middle-of-the-range light aircraft, which at a similar useage, works out at about £60/hr.
G